This application claims the right of foreign priority to German Application No. 100 07 024.8 filed on Feb. 16, 2000, and to European Application No. 00 116 129.8 filed on Jul. 31, 2000, and both applications are incorporated herein by reference in their entirety.
Interlinked production systems are used in mass production to be able to process workpieces in the most inexpensive and reliable manner in a number of processing stations. Typical applications for interlinked production systems are found in the automobile industry, for example for the highly efficient fabrication of motor and transmission components.
The line production is known as a classical example of an interlinked production system, in which the flow of parts between the individual processing stations is controlled over a belt, which serves as a buffer at the same time. Portals branch off to the side from the belt to the individual processing stations.
The coupling of a plurality of processing stations via portals is known as a further example of an interlinked production system, where belt buffer stores are arranged between the individual or several processing stations for decoupling. Such belt buffer stores are conveyor belts with which individual parts are conveyed or stored. Such buffers normally receive about 10 to 20 parts and can make up for certain fluctuations caused by delays at the associated processing stations.
However, a drawback is that the belt buffer stores are only designed for a small number of parts, so that when larger disruptions occur at one or more processing stations of the processing system, the entire system shuts down in short time. In addition, the handling of individual parts can have negative effects on their quality, because damage may occur. Furthermore, when emptying one of the buffers, one must first wait until all of the parts have been used up. This is a problem when a so-called one-piece-flow operation is important, i.e. when the processing steps are to be controlled so that one part passes through the various processing stations in sequence without being stored intermediately as far as possible. With a one-piece-flow operation, short throughput times are basically achievable, however, the productivity of the production system is reduced because the smallest machine idle time can lead to so-called linkage losses.
A one-piece-flow operation is practically impossible with the above-mentioned conveyor belt, through which the individual processing stations can be connected and coupled to one another through portals.
The use of a belt as conveying means and at the same time the use of buffering between the individual processing stations does allow a certain buffering with differing outputs of the individually coupled stations, however, the entire system cannot be designed for high productivity and short throughput times. The different cycle times of the individual stations necessarily negatively effect the output of the entire system.
Furthermore, the information flow associated with the individual parts is very difficult to control. This is especially a problem when the quality of the individual parts is to be fully documented.
When changing the two mentioned production systems to produce different parts, the entire system must at first be emptied before the fabrication of the other parts can begin. It is also basically known to couple so-called automated cells to one or more processing stations. A number of carriers for stacks of parts are contained in the cells which serve as buffers. With the coupled automated cells, the stations are supplied with fresh parts independent of the processing fluctuations and finished parts are received therein (see for example EP 0 673 711 A1 or EP 0 865 869 A1).
The coupling of all processing stations of the entire production system, for example having 20 or 30 stations, takes place from outerlying intermediate stores which are arranged between automated cells of the associated processing stations. Stacks of workpieces are transported by roller carts or wagons between these intermediate stores and the automated cells.
The higher requirement for storage and parts inventory for the entire system has proven to be a disadvantage. In addition, human intervention is required at the predetermined cycle intervals to promptly transport the stack of part carriers between the intermediate stores and the automated cells. This basic dependency on manual operations is considered to be at least partially disadvantageous in automated production systems.
It is also basically known to automatically couple different processing stations of an interlinked production system and the intermediately arranged buffers through transportation systems without a driver. The high investment and the complicated control and software for the total system has proven to be a disadvantage, where at the same time, an increased danger of accidents can occur. Furthermore, the reliability up until now has largely not been sufficient.
It is an object of the present invention to provide an improved interlinked production system which allowes a flexible control of the flow of the parts processed therein, even through a large system with several processing stations.
It is a further object of the present invention to provide an improved interlinked production system suitable for a one-piece-flow operation on the one hand and allowing operation using buffers for higher productivity on the other hand.
It is a further object of the present invention to provide an improved interlinked production system being as inexpensive as possible and flexible at the same time.
It is still another object of the present invention to provide an improved interlinked production system having a high reliability.
It is another object of the present invention to provide an improved interlinked production system requiring only a very limited space.
These and other objects of the present invention are achieved with an interlinked production system of the above-mentioned type, where in at least three buffers are provided, the buffers being configured to receive part carriers and having at least two stack positions, a transfer device being provided for transferring part carriers between the stack positions within the buffer. The object of the invention is completely achieved in this manner.
According to the present invention, the transportation of parts through the interlinked production system is ensured with the aid of one or more portals with portal grippers which are drivable thereon. The production system, which has at least three buffers, preferably however a plurality of buffers in communication with a corresponding number of processing stations, is flexibly interlinked through the buffers, which are configured to receive part carriers, whereby the disadvantages of belt stores are avoided. The capacity of the buffers can be adapted to the individual requirements and also to the given condition of the total system by the transfer device for transferring the part carriers between the stack positions within the buffer.
Human intervention is not necessary in the system for transporting the stacks of workpiece carriers. Rather, operating personnel is only necessary for the purposes of control and monitoring and for emergencies.
It is also possible, if desired to introduce additional part carriers into the buffers from the outside or to remove same. In this manner, an extremely flexible operation for the entire production system is made possible.
A one-piece-flow can be achieved in that the buffer capacity is not utilised or is minimised. Minimal throughput times and minimal stores can be achieved.
In another strategy, certain minimum capacities can be set for the buffers to achieve the highest possible productivity. At the same time it is possible to use specially configured buffers at various locations in the total system to account for differing machine cycle times, shorter machine idle times and even to account for changes in the production system. It is even possible to simulate the behaviour of the production system with the aid of a simulation and to determine optimal buffer capacities for the highest possible productivity, which are then used as set values in the individual buffers. Differing cycle times and the probability of failure of the individual components of the production system can be accounted for, to thereby optimise the total flow.
Furthermore, it is possible in emergencies to supply additional part carriers into the buffers or remove carriers therefrom through the outerlying transportation means without extensive use of personnel. The buffers can also be automatically loaded and unloaded according to the FIFO principle (first in/first out), which can generally take place in flexible manner or in predetermined time intervals.
A particular advantage of the system is also a decentralised administration of data, where the information concerning the individual parts, the part carriers or stacks of part carriers in the total system can be properly processed and monitored. The workpieces flow through the total system practically together with the associated information, and an extremely transparent flow of material and information results. Thus a transparency of the entire production flow results with an overview of the utilisation of the machines and the capacity of the buffers.
In a first embodiment of the present production system, at least one transfer device is formed by a portal gripper, which is configured to grip the parts and also to transfer the part carriers, where the stack positions of the buffer are arranged sequentially in the drive direction of the gripper along the portal.
This provides a particularly inexpensive and realisable solution because the buffers are very simply constructed and do not require their own transfer means. Moreover, the transfer takes place with the aid of grippers, which are used both for transferring part carriers and also for handling the parts, to introduce or to remove these from the processing stations and for loading these into the part carriers in the buffers and for unloading them. This particularly inexpensive configuration is offset by limited flexibility because a manual supply and discharge of additional part carriers in the buffers is no longer possible independently from the function of the remaining system. In addition, the various grippers can hinder one another. Idle times can also arise because the grippers cannot perform restacking within the buffer during supply to a processing station. Even so, this simplified configuration is sufficient for some systems due to its cost advantages.
According to another embodiment of the present invention, at least one of the buffers is configured as an automated cell having its own transfer device for transferring part carriers within the automated cell. In this manner, the above described disadvantages are avoided because restacking within the buffer becomes independent of the supply of parts to the processing stations.
The automated cells are preferably arranged such that the stack positions in the automated cells are located transversely to the extension direction of the at least one portal. In this manner, narrow automated cells can be arranged between adjacent processing stations to reduce the space requirement of the total system.
In a further embodiment of the present invention, at least one buffer is configured as an automated cell having a transfer device for transferring part carriers between different stack positions within a working space of the automated cell and having means for supplying and discharging stacks of part carriers into the working space and out of the working space.
In this manner, restacking and handling within the working space of the automated cell is decoupled from the supply or removal of workpiece carriers in a loading space. The automatic operations within the working space of the cell can be continued simultaneously with the supply and removal, where the necessary safety precautions are maintained by closing off the loading space when the outer door is open. For this purpose, each of the automated cells preferably comprises at least three stack positions.
In a further embodiment of the present invention, at least one of the buffers is coupled to the processing stations through at least two portals. In this manner, parts from a previous processing station can be transferred to a respective automated cell and parts can be transferred out of the automated cell into a subsequent processing station, without gripping means or the like within the automated cell hindering one another. Basically however, it would also be possible to provide only a single portal for connecting all of the processing stations and automated cells or buffers.
In a further embodiment of the present invention, the buffers are at least partially configured as automated cells, whereby a first, a second and a third stack position is arranged sequentially in a horizontal direction within the working space, which is closed to the top. The first stack position can be loaded through a door from the outside in horizontal direction and can be separated to avoid contact with the remaining stack positions. A transfer device extends in the direction of the sequentially arranged stack positions and allows a transfer of the parts between the three stack positions within the working space. The transfer device includes a first linear axis drivable in horizontal direction and a second linear axis drivable in vertical direction.
A sufficiently large buffer capacity can be realised for short cycle times of an associated processing station by using such an automated cell with low space requirements and relatively low costs. A transfer of part carriers between the individual stack positions as well as the readying of the part carriers for the associated gripper, which is drivable on a portal running thereabove, is achieved with a single transfer device. An additional loading unit, such as a stack changer module, is not necessary.
With this special strategy for transferring the part carriers between the individual stack positions, a more rapid working flow and a good adaptation to the associated stations can be realised with very short cycle times.
In a further embodiment, the first stack location is separated from the second neighbouring stack location through a substantially vertical bulkhead and is separated by a hood from the remaining portion of the working space to avoid contact, which is drivable at least between the first and second stack positions. The bulkhead can be configured to be stationary and provided with centering surfaces for guiding and centering part carriers supplied to the first stack position. In addition, the bulkhead can have associated guide elements which are arranged to engage the sides of the part carriers for centering the supplied part carriers.
The hood is preferably U-shaped and configured with a cover surface and two side surfaces. In addition, the hood is preferably provided to be drivable between the first, the second and the third stack positions. With these features, the handling within the working space can be decoupled from the supply or removal of part carriers from the first stack position. Furthermore, the automated cell can be designed for shorter cycle times.
The hood can be driven by means of the transfer device. However, an separate drive can be provided for the hood to achieve even shorter cycle times. The hood can also be configured to receive at least one part carrier, if an associated processing station has an especially short cycle time. For this purpose, the portal gripper at the third stack position can access the part carrier placed on the hood, while at the same time, a restacking between part carriers is possible at the first and second stack positions.
Finally, a drawer for receiving a part carrier is provided on the upper side of the hood, which allows a part carrier to be driven to the outside when the loading door is opened. This enables the supply and discharge of test parts and in addition an operation of the cell or the entire system only with individual part carriers placed in the hood and independently from the capacity of the buffers or automated cells. It is possible for example to briefly introduce a small series production into the work flow.
It will be understood that the above-mentioned features and those to be discussed below are not only applicable in the given combinations, but may also be used in other combinations or taken alone without departing from the scope of the invention.